Mesoarchean Subduction in the Pilbara Craton

Abstract

Two episodes of Mesoarchean subduction in the Pilbara Craton are attributed to interaction of the craton with another plate along its northwest margin. Northwest–southeast compression of the craton resulting from plate convergence is interpreted to explain the tectonic and magmatic evolution of the Northwest Pilbara Craton between 3160 and 2913 Ma. The first consequence of this convergence was the compression of the MORB-like basaltic crust of the Regal Basin as the adjacent Karratha and East Pilbara Terranes were forced closer together. Resulting failure of the thin crust of the basin established a subduction zone above which the volcanic arc of the 3130–3110 Ma Whundo Group was formed. Another consequence of the basin compression was obduction of a large section of its basaltic crust (Regal Formation) onto the Karratha Terrane. Eventual closure of the basin, marked by the 3070 Ma Prinsep Orogeny, ended the first episode of subduction. With ongoing convergence, the northwest plate began to be subducted under the northwest margin of the Pilbara Craton. This second episode of subduction lasted from about 3067 to 2913 Ma and resulted in the evolution of a series of continental magmatic arcs and retro-arc basins.